SOP: Polenske Value of Fats

GIFSQ — Global Institute for Food Safety & Quality

Principle

The Polenske value differs from the Reichert-Meissl value in that it is a measure of the steam-volatile but water-insoluble fatty acids — like caprylic, capric and lauric acids — present in oils and fats. The insoluble fatty acids retained on the filter paper during the R.M. distillation are dissolved in neutral alcohol and titrated with standard alkali.

Apparatus required

• Standard R.M.-Polenske-Kirschner distillation apparatus (as for the R.M. value determination)
• 9 cm Whatman No. 4 filter paper
• Dry flask

Reagents

a. Neutral ethyl alcohol.

b. 0.1 N NaOH.

c. Phenolphthalein indicator.

d. The distillate and the filter paper with the retained insoluble fatty acids from the R.M. value determination.

Procedure

Carry out the R.M. value determination up to the filtration of the distillate; the water-insoluble fatty acids are retained on the filter paper

↓

Dissolve the insoluble fatty acids by washing the condenser, the measuring cylinder, the 110 ml flask with stopper, and the filter paper containing the main bulk, each with 15 ml portions of neutral ethyl alcohol (45 ml in all)

↓

Collect the alcoholic washings in a clean dry flask and titrate with 0.1 N NaOH using phenolphthalein as indicator; run a blank determination without the sample

Calculation

Polenske value = (Sample titre − Blank titre) × N of NaOH × 10

Correction at high altitudes: as for the R.M. value, use:

                             (760 − 45)
Corrected Polenske value = Observed value × ─────────
                                              p − 45

Where,

• p = barometric pressure in mm of mercury at the place of determination

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.